Anyone knows what is the role of the blue & red Nuka-Cola caps?

And what's the difference between the 2 colors? (From demos it seems there are more red caps than blue ones) Or they have the very same role with different design only?

Well the Caps have always been a staple currency in the Fallout universe so I think it's safe to say that they are two different denominations of coin. Red=1 and Blue=5 is my guess.

If I had to guess, the Red ones are standard Nuka-Cola caps and the Blue ones are probably Nuka-Cola "Quantum" caps. In the video game, the latter is a far more beneficial and likely an even more refreshing beverage than the standard Nuka-Cola. But I'm going to agree with Fnoffen about how in practice, they probably just have different values. If we're lucky, they'll put out some Sunset Sarsaparilla star caps eventually and really set things off!

I was hoping for some VIM!